application of a PDS model to a new dataset obtained with a spectrometer A
[x_B_est] = pds_apply(model_pds,x_A)
a pds model obtained with the function pds_calc; a structure
spectra acquired with the spectrometer A; a div structure or a matrix of dimension (n x q)
the estimated spectra which would have been obtained on spectrometer B; a div structure
x_B_est.d is of dimensions (n x q)